Question: $ { \left[\begin{array}{rr}{3} & {4} \\ {0} & {2} \\ {0} & {4}\end{array}\right]-\left[\begin{array}{rr}{3} & {4} \\ {2} & {2} \\ {2} & {1}\end{array}\right] = {?} } $
Answer: To find the difference of two matrices, subtract the corresponding items between each matrix. ${\left[\begin{array}{rr}{3}-{3} & {4}-{4} \\ {0}-{2} & {2}-{2} \\ {0}-{2} & {4}-{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{0} & {0} \\ {-2} & {0} \\ {-2} & {3}\end{array}\right]}$